1. Field of the Invention
This invention relates to an olefinic thermoplastic elastomer composition (hereinafter, also referred to simply as xe2x80x9celastomer compositionxe2x80x9d). More particularly, this invention relates to an elastomer composition: that has sufficient mechanical properties, such as flexibility and elastic recoverability, and durability; that does not contaminate the surface of a molded article by the use of a softening agent, thereby avoiding environmental pollution; that has sufficient flame resistance using a small amount of flame retardant; that is superior in molding processability; and that is useful in various industrial fields, such as automotive interior/exterior parts, packing and housing of weak-electric products, watertight seats, gasket seals, and electric wire coating.
2. Discussion of the Background
Conventionally, olefinic thermoplastic elastomer compositions have been prepared by dynamically applying heat treatment, in the presence of a crosslinking agent, to rubber, olefinic resin, and softening agents such as paraffinic mineral oil, and the like. The step of processing the elastomer composition does not require vulcanization, and can be carried out according to the usual methods of processing thermoplastic resin, such as injection molding, extrusion molding, such as contour extrusion, calendering, and blow molding.
However, this elastomer composition is inferior in durability and does not have sufficient mechanical properties, such as flexibility and elastic recoverability, because the composition contains a softening agent. In addition, the softening agent causes bleedout to the surface of a molded article over time, and this might cause environmental pollution because of the vaporization thereof. In order to address these problems, studies have been made on the improvement in crosslinking density, the kind of rubber to be combined and the compounding ratios thereof, the kind of the softening agent and the content thereof, and the like. As a result, the durability, and the like, have been improved, but a new problem has occurred because the molding processability is lowered.
On the other hand, some elastomer compositions which have flame resistance have been conventionally prepared using various inorganic and organic flame retardants. However, in order to obtain sufficient flame resistance, normally a large amount of flame retardant of 200-300 parts by weight must be mixed with the elastomer. Disadvantageously, this lowers mechanical properties (such as flexibility and elastic recoverability) and durability. Another problem is that this kind of elastomer must be mixed with a large amount of softening agent (more than 20 parts by weight, for example) to maintain rubbery properties and loses its flame resistance due to the softening agent.
In order to solve these problems, in a technique of dynamically applying heat treatment in the presence of crosslinking agents, to rubber, olefinic resin, and softening agents such as paraffinic mineral oil, and the like, studies have been performed on the improvements in crosslinking density, the kind of rubber to be combined and the compounding ratio thereof, the kinds of flame retardants and softening agents and the content thereof, and the like. As a result, the durability, and the like, has been improved, but a new problem has occurred because the molding processability is lowered, and sufficient flame resistance cannot be easily obtained.
The molding processability can be improved by specifying the kind of olefinic resin, and the physical properties thereof, and the like. However, the use of such olefinic resin shows a tendency to lower the elastic modulus and raise hysteresis loss. Thus, it is not easy for the conventional olefinic thermoplastic elastomer composition to have sufficient flame resistance, mechanical properties, and durability, while environmental pollution is prevented, and also have excellent molding processability.
The present invention was made to solve the aforementioned conventional problems. It is an object of the present invention to provide an olefinic thermoplastic elastomer composition that is superior in flame resistance, mechanical characteristics, such as flexibility and elastic recoverability, and durability; that does not cause stains on the surface of a molded article nor environmental pollution which is caused by, for example, halogen containing flame retardants or paraffinic mineral oil as softening agents; and that also has excellent molding processability.
An olefinic thermoplastic elastomer composition according to a first aspect of the present invention is characterized in that it is produced in the presence of a crosslinking agent by applying heat treatment to a resin-rubber composition that contains an olefinic rubber and/or diene rubber, an olefinic resin, and a vinyl copolymer, wherein a vinyl monomer represented by the chemical formulae (1) or (2) is copolymerized in an amount of 20 percent by weight or more.
CH2xe2x95x90CHOCOR1xe2x80x83xe2x80x83(1)
CH2xe2x95x90CHOR2xe2x80x83xe2x80x83(2)
wherein R1 and R2 are each an alkyl group having a number of carbon atoms of 1-6.
An olefinic thermoplastic elastomer composition according to a second aspect of the present invention is characterized in that it comprises a heat crosslinked resin-rubber composition, produced in the presence of a crosslinking agent by applying heat treatment to a resin-rubber composition that contains an olefinic rubber and/or diene rubber, and an olefinic resin; and a vinyl copolymer, wherein a vinyl monomer represented by above mentioned chemical formulae (1) or (2) is copolymerized in an amount of 20 percent by weight or more, and wherein at least a part has not undergone heat treatment in the presence of the crosslinking agent.
An olefinic thermoplastic elastomer composition according to a third aspect of the present invention is characterized in that it is produced in the presence of a crosslinking agent by applying heat treatment to a resin composition that contains an olefinic resin and a vinyl copolymer, wherein a vinyl monomer represented by above mentioned chemical formulae (1) or (2) is copolymerized in an amount of 20 percent by weight or more.
An olefinic thermoplastic elastomer composition according to a fourth aspect of the present invention is characterized in that it comprises a heat crosslinked resin composition, produced in the presence of a crosslinking agent by applying heat treatment to a resin composition that contains an olefinic resin; and a vinyl copolymer, wherein a vinyl monomer represented by above mentioned chemical formulae (1) or (2) is copolymerized in an amount of 20 percent by weight or more, and in which at least a part has not undergone heat treatment in the presence of the crosslinking agent.
According to the present invention, an olefinic thermoplastic elastomer composition can be obtained which has sufficient mechanical characteristics, such as flexibility and elastic recoverability, and durability; which does not cause stains on the surface of a molded article nor environmental pollution which is caused by, for example, softening agents such as oils; and which also has excellent molding processability. The elastomer composition of the present invention may have more superior characteristics if the weight ratio between the olefinic rubber and/or diene rubber, olefinic resin, and vinyl copolymer is as stated in claim 2, 10, 18 or 26; if the weight ratio of crosslinking agents is as stated in claim 3, 11, 19 or 27; and if the weight ratio of flame retardants is as stated in claim 5, 13, 21 or 29.
Further, the elastomer composition of the present invention does not cause environmental pollution due to a smaller content of oils serving as a softening agent as stated in claim 7, 15, 23 or 31.